This invention relates to novel elastomeric materials derived from polymerization of mixtures of mono- and dilactones.
Polymers are finding increasing use in the field of medicine, particularly as substitutes for the natural materials of the body. In many cases, it is desirable that the polymer be degradable, to eliminate the need for recovery or removal. Biodegradable sutures derived from polyglycolic acid and polylactic acid are examples. Biodegradable polymers are also environmentally desirable, reducing problems of waste disposal and pollution. Most of the synthetic polymers which are biodegradable are either in the glassy state or are crystalline, with the result that very few elastomeric biodegradable materials are available for use. Such is the case for polyesters.
Homopolymers and copolymers of various cyclic esters such as glycolide, lactide, .delta.-valerolactone, and .epsilon.-caprolactone, have been the subject of numerous patents and scientific publications, including inter-alia U.S. Pat. Nos. 2,362,511; 2,758,987; 2,890,208; 3,021,309; 3,169,945; 3,284,417; 3,297,033; 3,463,158; 3,531,361; 3,620,218; 3,636,956; 3,736,646; 4,045,418 and 4,057,537.
Polyglycolide is reported to be a hard, tough, crystalline polymer with a melting point of about 224.degree.-226.degree. C. and a glass transition temperature (T.sub.g) of 36.degree. C. as noted in the aforementioned U.S. Pat. No. 3,297,033. The polymer from DL-lactide is a tough, amorphous solid with a T.sub.g of about 57.degree. C. The polymer from L-lactide is a tough partially crystalline solid, m.p. 180.degree. C. Poly (.epsilon.-caprolactone) is described as a tough, partially crystalline solid melting at 63.degree. C., T.sub.g =-60.degree.. Sinclair in U.S. Pat. Nos. 4,045,418 and 4,057,537 describes copolymers of .epsilon.-caprolactone and either L-lactide or DL-lactide as rigid, clear, thermoplastic solids. None of the above homopolymers and copolymers, and polymers of structurally related mono-lactones is elastomeric. However, elastomeric properties can be introduced by curing the polylactone with a peroxide such as dibenzoyl peroxide at an elevated temperature as demonstrated for example in U.S. Pat. No. 4,057,537 noted above. However, the exact structures of so-cured polymers are unknown and the property of degradation to known monomer products in vitro or in vivo is lost in this process. This reduces the biomedical value of such materials.
Accordingly, it is the primary object of the present invention to provide elastomeric lactone polymers designed to achieve different degrees of permeability, elasticity, and rates of biodegradation.
It is a further object of the present invention to provide polymers suitable for the controlled delivery of medicinal agents.
Still yet another object of our invention is to provide improved surgical aids and temporary artificial biomaterials.
These and other objects of the present invention will become more apparent from the discussion which follows.